(1) Field of the Invention
The invention generally relates to a chemical mechanical polishing process used in semiconductor manufacturing and, more particularly, to a pad conditioner used to remove build up of residue and slurry from an abrasive polishing pad during a chemical and mechanical polishing process of a semiconductor wafer.
(2) Description of Prior Art
Semiconductor fabrication often uses a combination of chemical and mechanical polishing (CMP) to reduce the thickness and planarize a thin film coating on a wafer. Typically, the wafer is placed in a polishing head and makes contact with a rotating polishing pad having a slurry applied thereto. Often the polishing head holding the wafer also rotates making the planarization process more uniform.
FIGS. 1a and 1b illustrate schematically the current art for the CMP process. FIG. 1a shows a cross section of the CMP process, while FIG. 1b shows a more simplified top view. The wafer (not shown) is contained laterally by a wafer carrier 106. To facilitate thin film planarization, uniform pressure is applied mechanically from above to the carrier 106 holding the wafer firmly against the polishing pad 100. The polishing table 102 and polishing pad 100 are rotated at a set speed about axis A2 by adjusting the polishing table drive mechanism 104. The carrier drive mechanism 108 will rotate the wafer carrier 106 about axis A1 at a second predetermined speed. During the CMP process an abrasive and chemical slurry 116 is dispensed through a spigot 110. During the polishing operation residue from the wafer and particles in the slurry 116 build up in pores of the pad 100. Over time this reduces the thin film removal rate and can result in yield loss. For this reason, the pad is periodically conditioned. The conditioner 112 typically having a diamond abrasive crystal electroplated to the lower surface (not shown) is pressed against the pad 100 while being moved radially across the pad 100 and rotated about axis A3 by the conditioner drive mechanism 114. This conditioning operation can be performed while a wafer is being polished, but often is performed as a separate step with de-ionized (DI) water applied to the pad. The conditioning process is only performed when needed because constant contact of the conditioner 112 and pad 100 would cause the pad 100 to wear out prematurely.
Referring now to FIG. 2 illustrating in cross section the current art for pad conditioning. Here a conditioner 112 having a flat, diamond abrasive crystal lower surface 118 is pressed against the pad 100. The diamond crystals 118 are usually electroplated to a nickel alloy conditioner 112. Unfortunately, this arrangement causes the conditioning to occur non-uniformly which in turn results in non-uniform material removal from the wafer. The non-uniform conditioning is caused by two factors. The first factor is due to the increased friction at the leading (left) edge of the conditioner 112. This additional friction results from the relative motion between the pad 100 and conditioner 112. The second factor is that, due to the shape of the conditioner 112, the slurry (not shown) used during the conditioning process (typically DI water) will not reach the center of the conditioner 112. One other problem with this pad conditioning method is that the low pH slurry attacks the diamond crystals 118 causing particles to fall off and subsequently scratch the wafers.
Other approaches attempt to address problems with pad conditioning and maintaining polishing uniformity. U.S. Pat. No. 5,605,499 to Sugiyama et al. teaches a method using a specific polishing pad along with an oscillating conditioning tool which has a shape designed to conform to the shape of the backing film used on the wafer carrier. U.S. Pat. No. 5,667,433 to Mallon teaches a method using keys to locking the conditioner in place thereby eliminating slippage of the conditioner. U.S. Pat. No. 5,823,854 to Chen teaches a method utilizing an automated measuring process to determine when the polishing pad needs conditioning. U.S. Pat. No. 5,904,615 to Jeong et al teaches a method using a disc or cup shaped conditioner while providing ultrasonic vibration to the conditioner. U.S. Pat. No. 5,906,754 to Appel et al teaches a method where polishing and conditioning are performed simultaneously. There are three embodiments of this invention using conditioners with a lower surface having triangular teeth, rectangular teeth and dimples, respectively.